Process and composition for coating metals

Abstract

Method and composition for applying an organic coating to a metallic surface, the surface being contacted with an acidic aqueous coating composition comprising an organic coating-forming material, fluoride, and ferric iron, wherein the thickness and/or weight of the coating formed on the surface can be controlled by varying the time the surface is immersed in the composition.

We claim: 
     
       1. In a process wherein a resinous coating is applied to a metallic surface by contacting it with an acidic aqueous coating composition which chemically attacks said surface and dissolves metal therefrom, said composition containing dispersed solid particles of resin and dissolved ferric iron, the source of the ferric iron including a source other than said metallic surface, the improvement comprising effecting the formation of said coating with said composition having incorporated therein dissolved fluoride, said composition containing said dissolved fluoride being capable of forming on a metallic surface immersed therein, and in a substantially electrostatic field-free environment, a resinous coating which increases in amount during at least a portion of the time said surface is immersed in said composition. 
     
     
       2. A process according to claim 1 wherein said surface is contacted with said composition by immersing it in the composition and wherein said surface is a ferrous surface. 
     
     
       3. A process according to claim 2 wherein a source of said dissolved ferric iron is a readily soluble ferric iron-containing compound. 
     
     
       4. A process according to claim 3 wherein said readily soluble compound is ferric chloride, ferric nitrate, ferric sulfate or ferric fluoride. 
     
     
       5. A process according to claim 2 wherein a source of said dissolved ferric iron includes a partially soluble ferric iron-containing compound. 
     
     
       6. A process according to claim 5 wherein said partially soluble compound is ferric phosphate or ferric oxide. 
     
     
       7. A process according to claim 5 including first aging fine particles of said partially soluble compound in water and thereafter immersing said ferrous surface in said composition. 
     
     
       8. A process according to claim 2 wherein said resin is selected from the group consisting of styrene-butadiene, acrylic, ethylene-vinyl acetate and polyethylene resins. 
     
     
       9. A process according to claim 2 wherein said dispersed resin particles are anionically stabilized. 
     
     
       10. A process according to claim 2 wherein said composition includes a nonionic surfactant for maintaining said particles dispersed in the composition. 
     
     
       11. A process according to claim 2 wherein said composition contains hydrofluoric acid. 
     
     
       12. A process according to claim 2 wherein the source of said ferric iron is ferric fluoride and the acid of said composition is hydrofluoric acid. 
     
     
       13. A process according to claim 2 including an oxidizing agent containing oxygen. 
     
     
       14. A process according to claim 1 wherein said resin particles are anionically stabilized, wherein said source of dissolved ferric iron is ferric chloride, ferric nitrate, ferric sulfate, ferric fluoride, ferric oxide or ferric phosphate and wherein said composition includes nitric, sulfuric, hydrochloric, hydrofluoric, phosphoric, acetic, chloracetic or trichloracetic acid. 
     
     
       15. A process according to claim 14 wherein said surface is immersed in said composition. 
     
     
       16. A process according to claim 1 wherein the source of said dissolved ferric iron is ferric fluoride, wherein said composition includes hydrofluoric acid and wherein said composition includes an anionic surfactant for maintaining said particles dispersed in the composition. 
     
     
       17. A process according to claim 16 wherein said surface is immersed in the composition. 
     
     
       18. A process according to claim 17 wherein said surface is a ferrous surface. 
     
     
       19. In a process wherein a resinous coating is applied to a metallic surface by contacting it with an acidic aqueous coating composition containing dispersed solid particles of resin, dissolved fluoride and an oxidizing agent, wherein said composition chemically attacks said surface and dissolves metal therefrom, and wherein said oxidizing agent is effective in increasing the rate at which the composition dissolves metal, and wherein said composition is capable of forming on a metallic surface immersed therein a resinous coating which increases in amount during at least a portion of the time said surface is immersed in said composition, said composition being effective to form said resinous coating in a substantially electrostatic field-free environment, the improvement comprising effecting the formation of said coating with said composition having incorporated therein dissolved ferric fluoride oxidizing agent, the source of the ferric including a source other than said metallic surface. 
     
     
       20. A process according to claim 19 wherein said composition includes also an oxidizing agent containing oxygen. 
     
     
       21. A process according to claim 19 wherein said composition includes an anionic surfactant for maintaining said particles dispersed in the composition, and wherein said composition is prepared from ferric fluoride and hydrofluoric acid. 
     
     
       22. A process according to claim 21 wherein said surface is contacted with said composition by immersing it in the composition and wherein said surface is a ferrous surface. 
     
     
       23. A process according to claim 19 wherein said surface is contacted with said composition by immersing it in the composition. 
     
     
       24. In a process wherein a resinous coating is applied to a metallic surface by contacting it with an acidic aqueous coating composition containing a dispersion of solid particles of resin stabilized by an anionic surface active agent, wherein said composition chemically attacks said surface and dissolves metal therefrom, the improvement comprising effecting the formation of said coating with said composition having incorporated therein dissolved ferric iron and fluoride, the source of the ferric iron including a ferric-containing compound which is soluble in the composition and from a source other than said metallic surface, said composition containing said dissolved ferric iron and fluoride being capable of forming on a metallic surface immersed therein, and in a substantially electrostatic field-free environment, a resinous coating which increases in amount during at least a portion of the time said surface is immersed in said composition. 
     
     
       25. A process according to claim 24 wherein said composition includes ferric fluoride and hydrofluoric acid and wherein said surface is a ferrous surface which is contacted with said composition by immersing the surface in the composition. 
     
     
       26. A process according to claim 25 wherein said particles of resin are styrene-butadiene resin and wherein said composition includes carbon black pigment. 
     
     
       27. In a process wherein a resinous coating is applied to a metallic surface by immersing it in an acidic aqueous coating composition which chemically attacks said surface and dissolves metal therefrom, said composition containing dispersed solid particles of resin and a material which is effective in increasing the rate at which the composition dissolves metal, and wherein said composition is capable of forming on a metallic surface immersed therein a resinous coating which increases in amount during at least a portion of the time said surface is immersed in said composition, said composition being effective to form said resinous coating in a substantially electrostatic field-free environment, the improvement comprising effecting the formation of said coating with said composition having incorporated therein dissolved ferric fluoride which is effective in increasing the rate at which metal is dissolved from said surface, and said composition being substantially free of an oxygen-containing oxidizing agent in an amount which effects a further increase in the rate at which metal is dissolved from said surface. 
     
     
       28. A process according to claim 27 wherein the source of the ferric in said composition is ferric nitrate, ferric sulfate, ferric chloride, ferric oxide or ferric phosphate and wherein the source of said fluoride includes hydrofluoric acid. 
     
     
       29. A process according to claim 27 wherein the dissolution of said metal surface is effected substantially exclusively by the acid and dissolved ferric fluoride constituents of the composition and wherein said composition includes an anionic surfactant for maintaining said particles dispersed in the composition. 
     
     
       30. A process according to claim 29 wherein the acid of said composition is hydrofluoric acid only. 
     
     
       31. A process according to claim 29 wherein said surface is a ferrous surface. 
     
     
       32. A process according to claim 30 wherein said surface is a ferrous surface. 
     
     
       33. A process according to claim 32 wherein said resin is styrene-butadiene resin. 
     
     
       34. A process according to claim 27 including withdrawing the resinous coated surface from said composition, exposing the coated surface to air for a time of about 15 seconds to about 10 minutes and thereafter rinsing the coated surface with water. 
     
     
       35. A process for forming a resinous coating on a ferrous metal surface comprising immersing the surface in an acidic aqueous coating composition which chemically attacks said surface and dissolves iron therefrom, said composition containing dispersed anionically stabilized resin particles of styrene-butadiene, hydrofluoric acid and dissolved ferric fluoride, said ferric fluoride being effective to increase the rate at which iron is dissolved from said surface, said composition being substantially free of amounts of other materials which would effect a further increase in the rate at which iron is dissolved from said surface, said composition forming on said surface while immersed therein and in a substantially electrostatic field-free environment a resinous coating which increases in amount during at least a portion of the time said surface is immersed in said composition, and withdrawing the resinous coated surface from said composition. 
     
     
       36. A process according to claim 35 wherein said composition includes an anionic surfactant for maintaining said particles dispersed in the composition. 
     
     
       37. A process according to claim 36 wherein said composition includes carbon black pigment.